Washington ? The Air Force said Friday it has punished 70 airmen involved in the accidental cross-country flight of a nuclear-armed B-52 bomber following an investigation that found widespread disregard for the rules on handling such munitions.

“There has been an erosion of adherence to weapons-handling standards at Minot Air Force Base and Barksdale Air Force Base,” said Maj. Gen. Richard Newton, the Air Force deputy chief of staff for operations.

Newton was announcing the results of a six-week probe into the Aug. 29-30 incident in which the B-52 was inadvertently armed with six nuclear-tipped cruise missiles and flown from Minot in North Dakota to Barksdale in Louisiana without anyone noticing the mistake for more than a day.

The missiles were supposed to be taken to Louisiana, but the warheads were supposed to have been removed beforehand.

A main reason for the error was that crews had decided not to follow a complex schedule under which the status of the missiles is tracked while they are disarmed, loaded, moved and so on, one official said on condition of anonymity because he was not authorized to speak on the record.

The airmen replaced the schedule with their own “informal” system, he said, though he didn’t say why they did that nor how long they had been doing it their own way.

“This was an unacceptable mistake and a clear deviation from our exacting standards,” Air Force Secretary Michael W. Wynne said at a Pentagon press conference with Newton. “We hold ourselves accountable to the American people and want to ensure proper corrective action has been taken.”

Rep. Ellen Tauscher, D-Calif., chairwoman of the House Armed Services strategic forces subcommittee, said she believed the Air Force had done a thorough investigation, but the findings were “a warning sign that there has been degradation” of attitudes toward the handling of the weapons.

“These are not just rules that people dreamed up … just so they could check off the boxes,” she said. “This is fundamentally important to the security of the country and the world.”

Hans Kristensen of the Federation of American Scientists was among those skeptical that the August flight represented an isolated incident.

He said a decline in Air Force standards for nuclear weapons maintenance and security was documented by the government a decade ago.

Newton acknowledged that the Air Force needs to “restore the confidence” lost among the American people after the August incident, which raised questions about the safety of the country’s nuclear arsenal.